Articulated rail cars are well known in the railway art, and generally comprise a pair of rail car platforms arranged end-to-end with the mutually adjacent ends thereof supported by a common truck. For example, a center plate portion of one platform connector element may be supported on the bolster center plate of a conventional three piece truck in the usual manner. The truck bolster center plate surface supports and laterally retains the corresponding center plate bearing surface of one car platform connector element, and the other car platform connector element engages the first mentioned platform connector element to provide a flexible connection therebetween.
In the prior art, the flexible connection between the adjacent ends of the two car platforms, and their retention with respect to a common truck, has often been achieved through employment of an articulating joint assembly including complex and precisely aligned, nested bearing elements having spherical engagement surfaces to provide the necessary three rotational degrees of freedom to accommodate relative pitch, yaw and roll movement of the connected car platforms with respect to each other. In one such prior articulating connector, one of the two adjacent platform ends is supported on a truck bolster center plate surface as noted above. The other of the two platform ends is supported vertically by a spherical bearing segment that nests above the center plate of the first mentioned platform end. Longitudinal train action forces are transmitted between the two platforms through other sets of spherical segments which share a common center of rotation with the spherical segment that provides the vertical support.
Examples of known articulating connection assemblies are shown in U.S. Pat. Nos. 3,399,631, 3,646,604 and 3,716,146. My prior U.S. Pat. No. 4,962,861 discloses an articulating connector unlike such conventional articulating connectors as those characterized hereinabove, and in which the requisite three relative degrees of rotational freedom are not required to share a common center of rotation.
A common feature of many articulating connectors is a vertically extending pivot pin which is used to assemble and locate the various spherical bearing segments with a common center. These spherical bearing surfaces transmit buff and draft loads between the connected car platforms; however, the draft loads sustained by prior articulating connectors also have been transmitted between the connected platforms by the vertically extending pin. Thus, the loads borne by prior articulating connectors are transmitted through both the concentrically nested spherical bearing surfaces and the generally cylindrical bearing surfaces of the pin. For proper connector operation, all of these bearing surfaces must maintain their concentric alignment and position.
Conventional articulating connectors commonly are rather complex structures, typically including, as has been noted, both the cylindrical center pin and an arrangement of spherical bearing surface segments in the male and female connector elements for carrying buff and draft loads. Specifically, the primary active bearing surface of the male connector member of prior articulating connectors may be a convex spherical or concave spherical bearing surface, depending on whether the load being borne is a buff or a draft load. Similarly, the primary active bearing surface of prior female connector members may be either an essentially cylindrical surface engaging the cylindrical center pin for draft loads, or a concave spherical bearing surface for buff loads.
Due to the number of separate parts, including bearing segments, which make up conventional articulating connector assemblies, their inherent complexity, and the required level of manufacturing precision, known articulating connectors currently in revenue service have been costly to manufacture and difficult to assemble and disassemble, and in addition have been difficult to maintain and service. Concerning this latter difficulty, critical wear patterns on the spherical bearing interfaces which transfer the loads between the ends of the interacting platforms can cause the connector to bind or lock.
The longer and more heavily loaded container platforms of modern articulated cars typically require 125 ton trucks. Each platform can carry two or more containers, often stacked two high, to achieve maximum volume capacities. Under such loading conditions, each truck supporting the adjacent ends of two platforms must bear up to 140,000 pounds of vertical center plate load. With these heavier center plate loads and greater utilization overall, prior articulating connectors can sustain sufficient wear, including bearing surface galling, during relatively short periods of revenue surface to cause connector components to bind or lock, with resultant severe hinging restraint between adjacent platforms. Horizontal hinging restraint can precipitate rail roll-over on curves, resulting in derailment.
Wear in prior connectors has also caused reduced vertical side bearing clearance resulting in the need for frequent side bearing clearance adjustment. Additionally, progressive wear from longitudinal forces can produce asymmetry among the various engaged spherical bearing elements of an articulated connector, even in connectors that can compensate for wear accumulation, with possible resultant binding and galling at the interfacing bearing surfaces.